Abstract
The genetic conflict between parents and their offspring is a cornerstone of kin selection theory and the gene-centred view of evolution, but whether it actually occurs in natural systems remains an open question. Conflict operates only if parenting is driven by genetic trade-offs between offspring performance and the parent's ability to raise additional offspring, and its expression critically depends on the shape of these trade-offs. Here we investigate the occurrence and nature of genetic conflict in an insect with maternal care, the earwig Forficula auricularia. Specifically, we test for a direct response to experimental selection on female future reproduction and correlated responses in current offspring survival, developmental rate and growth. The results demonstrate genetic trade-offs that differ in shape before and after hatching. Our study not only provides direct evidence for parent–offspring conflict but also highlights that conflict is not inevitable and critically depends on the genetic trade-offs shaping parental investment.
Highlights
The genetic conflict between parents and their offspring is a cornerstone of kin selection theory and the gene-centred view of evolution, but whether it occurs in natural systems remains an open question
We focused on the former and tested the three above predictions using a large scale and replicated selection experiment in an insect with extended maternal care, the earwig Forficula auricularia
F. auricularia is an ideal system for this study: the species reproduces sexually, females care for eggs and hatched nymphs, and they produce up to two clutches in their lifetime[22,23,24]
Summary
The genetic conflict between parents and their offspring is a cornerstone of kin selection theory and the gene-centred view of evolution, but whether it occurs in natural systems remains an open question. While genetic trade-offs provide evidence for antagonistic parent– offspring co-evolution, they per se are not sufficient evidence for parent–offspring conflict over the amount of PI This conflict occurs when PI fitness optima differ for parent and offspring[2,7,14], a condition requiring sexual reproduction and depending on the shape of the genetic trade-offs. It is only occasionally reached when offspring fitness gains show constant or accelerating returns, but always met under diminishing returns, that is, when offspring stand to gain less from an additional unit of investment when they are already in good than when they are in poor condition (Fig. 1)[2,4,5,18]. We selected females with low expectation of future offspring (that is, Small relative size of (or no) second clutch; S-lines), high expectation of future offspring (that is, Large relative size of second clutch; L-lines) and intermediate expectation of future
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